Please explain the difference between canceling AF and AF lock... If I use AF via shutter half-press and get focus confirmation beep and a red viewfinder overlay blinks on the focus point then AF system has focused on something. If I then press the AF button, canceling AF and neither the subject nor I move (as would hopefully be the case if I were using this configuration of the AF button while in AF-C mode to facilitate focus-recompose) then the focus is maintained.

Similarly AE-L just holds an AE setting. Cancel AF freezes a focus setting that was could include an accurate focus setting for a desired object.

Use of the lock terminology means more to me in live view where focus tracking is used and the AF system is 'locked' onto a specific moving target.

When you press the AF button, and C2.13 is set to Cancell AF, the camera switches to MF Manual Focus for as long as you press the AF button. The Viewfinder shows exactly that - "MF".

Physically your lens has not moved, so in that sense "Focus is Maintained", physically.

However, when you switch to MF (really what you are doing by pressing the Cancell AF button), the camera's electronics has lost its autofocus setting, and in the process you have also lost the AE-lock that you set linked to AF.

More to the point though, my original post should've been 'how can i do focus recompose in AF-C?'. I'm guessing the answer is to give up on the AF button and staying in AF-C but instead simply switch AF mode to AF-S?

'how can i do focus recompose in AF-C?' -

I suppose the reason you use AF-C is you want to do focus tracking, just that when you actually want to take the shot, you want to recompose ?